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Question 20N.2.HL.TZ0.c

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Date November 2020 Marks available [Maximum mark: 7] Reference code 20N.2.HL.TZ0.c
Level HL Paper 2 Time zone TZ0
Command term Discuss Question number c Adapted from N/A
c.
[Maximum mark: 7]
20N.2.HL.TZ0.c

More than 8 million different species are alive today but over the course of evolution, more than 4 billion may have existed.

Discuss the process, including potential risks and benefits, of using bacteria to genetically modify plant crop species.

[7]

Markscheme

Process:
a. genetic modification by gene transfer between species;

b. gene/Bt gene/DNA segment transferred from bacterium to plant/crop;

c. gene/DNA codes for/responsible for desired protein/gene product;

d. bacteria have/produce plasmids / gene/DNA inserted into plasmid;

e. using restriction enzymes/endonucleases to cut DNA;

f. using DNA ligase to join DNA;

g. bacterium transfers (modified) plasmid to plant cell;

Benefits:
h. increase crop yields / more food produced / less land needed to grow food;

i. increase pest/disease resistance / use less pesticides/insecticides/fungicides;

j. improves crops to be more nutritious/increased vitamin content;

k. increased tolerance to saline soils/drought/high temperatures/low temperatures;

Risks:
l. GM organisms could spread to sites (where they will cause harm);

m. transferred gene could spread to other species / spread of herbicide resistance to weeds;

n. GM crops that produce pesticide could kill non-pest insects/monarch butterflies / insect pests could develop resistance to pesticides/insecticides/Bt toxin;

Examiners report

This part of the question was also poorly answered by many candidates. Only a simple account of the procedures used to genetically modify plants was expected and not the details of the use of Agrobacterium that are part of Option B. There was confusion among many candidates about how bacteria might be involved in genetic modification of plants. Two possibilities that were rewarded were the transfer of genes from bacteria or of plasmids derived from bacteria. Where marks were scored, they were mostly for risks and benefits, but many accounts of these were unconvincing. Some of the risks that were suggested were not evidence-based. As with vaccination, it is important that myths about the dangers of procedures such as genetic modification are not propagated.

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